Normally, containers for products, such as beverages, sanitary articles and the like, are provided with an imprint for identifying the product and/or for high-quality product presentation. The imprint may be applied directly to the outer surface of a container and/or to a label as additional print and it may comprise e.g. characters, logos, patterns and color gradients. For applying the imprint, the containers are normally conveyed by a transport unit, e.g. a carousel, and, while being conveyed, they are printed on e.g. with light-curing printing inks by means of direct printing heads. For multi-color printing, the container treatment machine may have arranged thereon a plurality of direct printing heads with printing inks of different colors.
The initially liquid printing ink is irradiated on the containers, e.g. with UV light by means of a curing unit arranged on the carousel in a stationary manner, and is thus cured. The container treatment machine may comprise a plurality of curing units, which cure the printing ink after printing of a respective color. Alternatively, it is also imaginable that the curing unit is arranged downstream of all the direct printing heads, when seen in the conveying direction, so that the printing inks of all colors are cured simultaneously. Finally, also a combination is imaginable, in the case of which a so-called pinning (initial curing) is carried out, e.g. with UV LEDs after each printing head, and the whole imprint is then hardened at the end.
The above is, however, disadvantageous insofar as direct light radiation or scattered light of the curing unit falls onto the direct printing heads where it inadvertently cures the printing ink. The nozzles of a direct printing head may thus clog and/or the print quality of direct printing may be impaired.